Electric power transmission and distribution systems or networks comprise high-voltage tie lines for connecting geographically separated regions, and substations for transforming voltages and for switching connections between lines. Power generation and load flow in a network with several substations is controlled by a central energy management (EMS) system. Protection of network components, in particular lines, is achieved by control devices and methods, and in particular by protection devices that continuously measure e.g. currents, voltages, temperatures etc. locally and locally disconnect lines or other components when these measurements indicate an emergency, overload or fault condition. Such protection devices are e.g. overcurrent relays, differential protection devices, phase comparison relays or distance protection relays.
Due to very high reliability requirements, protection devices with associated measurement and communication units are often implemented redundantly. This increases the overall system cost accordingly. It is therefore desirable to provide redundant protection functions at a lower cost.